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"God forbid we should ever be twenty years without such a rebellion.... And what country can preserve its liberties, if its rulers are not warned from time to time, that this people preserve the spirit of resistance? Let them take arms.... The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants." - Thomas Jefferson, in letter to William S. Smith, 1787

3-4 gallons is nothing. They can support a lot more weight. The only problem is that it takes forever to bring a batch to boil. The advantage is that they are much easier to clean in the event of a boil-over. Sometimes I'll boil my strike water on the stove to save on propane and I used to do extract batches on it, so it is definitely doable. Another good thing about glass stove-tops is that you can slide your kettle off the burner to reduce heat quickly, without having to lift it up...very useful to control the heat!